Murder Princess Manga by Sekihiko Inui

The world of politics is treacherous enough. In Foreland, it's deadly confusing. When her royal father is murdered by a greedy drug manufacturer, Princess Alita must step forward to take over the kingdom - but who is the real princess. Don't ask her. A freak magical mishap has trapped her in the body of Falis, the bounty hunter. Now Alita must rule disguised as a servant while the battle-savvy Falis sits on the throne in her body. And as if this weren't enough to juggle, the evil Professor Akamashi and his twin android assassins just HAVE to cause trouble.